1. Field of the Invention
This invention relates to a control grid subassembly as well as to a method of forming a grid assembly for an electron gun having particular utility in a multibeam cathode ray tube.
2. Description of the Prior Art
Multibeam cathode ray tubes are available which employ a plurality of individually controlled electron beams that are directed to the tube's phosphor screen to provide the predetermined display. Typically the electron gun in such a tube includes a cathode which emits electrons and a grid assembly which divides the electrons into many separately controlled electron beams or streams of electrons and includes a plurality of separate control grid elements each containing a passage therethrough for permitting passage of an electron beam when the control grid is at a certain electrical potential or voltage applied through external circuits but which prevents the passage of the electron beam if a predetermined different electrical potential is applied to that grid.
Such grid assemblies have been fabricated by aligning together previously formed pierced or drilled parts using dowel pins and then clamping the parts together with nuts and bolts or by glass beading or by cementing using silica-alumina dental cements. The minute electron beam passages in each grid have typically been formed by drilling individual holes mechanically and by photoetching techniques. As a result, grid assemblies made by those methods require very precise parts. The assembly of those grid assemblies depends upon the maintenance of close tolerances in fit and in alignment between the component parts or elements of the grid assembly and the alignment dowel pins. As a result, grid assemblies for multibeam cathode ray tubes obtained by such methods have a degree of variation in performance in respect to array geometry modulation characteristics and beam diameter from one grid assembly to another.